video freezes, audio plays

my problem is this- whenever I try to open any video file the audio will play but the video (along with windows) will be frozen. as in the video won't play at all and windows will be incredibly slow and it's impossible to do anything until the video finishes- then everything unfreezes.

my configuration:
pentium 4
nvidia 6600

I tried several forceware drivers, that didn't change anything. Even tried installing coolbits 2.0 to enable the editing of advanced options and set render advanced frame to "0". I have the following codecs installed -klite, realalt. All my drivers seem to be working properly as in there are no :unindentified devices" or anything. Except for that problem everything else works fine including 3d games.